In place of specific chlorofluorocarbons designated as strong ozone-depleting substances by the Montreal Protocol agreed in Canada in 1987, various alternative fluorocarbons with less fear of ozone depletion are synthesized and used. In recent years, the alternative chlorofluorocarbons are also required to show a shorter life in the air and less fear of global warming.
It is known that 2-chloro-1,3,3,3-tetrafluoropropene, which has a double bond in its molecule, gets quickly decomposed by reaction of the double bond with OH radial etc. in the air and thereby shows a low global warming potential and less fear of global warming. There exist trans and cis geometric isomers of 2-chloro-1,3,3,3-tetrafluoropropene. Hereinafter, the trans and cis isomers of 2-chloro-1,3,3,3-tetrafluoropropene is sometimes referred to as “1224E” and “1224Z”, respectively; and 2-chloro-1,3,3,3-tetrafluoropropene is sometimes simply referred to as “1224” in the case where there is no need to distinguish the trans and cis isomers or in the case where it refers to a mixture of the trans and cis isomers. The boiling point of 1224E is 23° C., whereas the boiling point of 1224Z is 17° C. Both of 1224E and 1224Z have a boiling point in the vicinity of room temperature (about 20° C.) and can suitably be used as blowing agents, solvents, coolants, working fluids or the like.
In the case of using 1224 as a blowing agent for a heat insulating material, low-boiling 1224Z is suitably usable for a heat insulating material in a refrigerator; and high-boiling 1224E is suitably usable for a heat insulating material in a building because of its good handling properties.
As the boiling point of 1224 is in the vicinity of room temperature, 1224 can also suitably be used as a heating medium for a heat pump or a high-temperature working fluid. In the case of using 1224 as a high-temperature working fluid for a heat pump, the coefficient of performance (COP) of the heat pump, which indicates cooling/heating capacity per 1 kW of power consumption, and the heat transfer capacity of the heat pump in freezing cycles etc. vary with even a slight difference in boiling point of the working fluid. In the case of using 1224 as a high-temperature working fluid, the suitable boiling point of the working fluid varies depending on the conditions of thermal cycles. It is thus preferable to appropriately select and use either the trans isomer (1224E) or the cis isomer (1224Z) according to the purpose of use.
In the following Patent Documents 1 and 2 and Non-Patent Document 1, there are disclosed processes of forming 1224.
Patent Document 1 discloses a process for purifying a (E)-1-chloro-3,3,3-trifluoropropene composition, which contains at least hydrogen fluoride and 2-chloro-1,1,1,3,3-pentafluoropropane, by contact with a weak base. More specifically, this process includes the step of bringing trans-1-chloro-3,3,3-trifluoropropane (sometimes abbreviated as “1233E”) containing hydrogen fluoride and 2-chloro-1,1,1,3,3-pentafluoropropane (sometimes abbreviated as “235da”) as a trace impurity into contact with the weak base so as to remove hydrogen fluoride and 235da and obtain 1233E as a purified product without forming 1224.
Non-Patent Document 1 discloses, as a specific synthesis example of 1224, a method for forming 2,3-dichloro-1,1,1,3-tetrafluoropropane (sometimes referred to as “234da”) by photochlorination of 1,3,3,3-tetrafluoropropene (sometimes referred to as “1234”), and then, forming 1224 by dehydrochlorination of 234da in a potassium hydroxide solution. Herein, 234da is a hydrochlorofluorocarbon represented by CF3CHClCHClF.
Further, Patent Document 2 discloses a method for forming 235da as a raw material of 1224.